A typical electronic system (computer system or server system) usually comprises three main components: a Central Processing Unit (CPU), hard disks and memories. Hard disks are one of the most important storage devices outside the system (among other auxiliary storage devices including floppy disks, compact discs, flash memories, magnetic tapes and so on) that form the data storage center for the entire system and store a majority of data and programs used when system operates. Hard disks can be divided into two types according to their interfaces: the traditional Parallel Advanced Technology Attachment (PATA) hard disks and the new Serial Advanced Technology Attachment (SATA) hard disks. Since the PATA hard disks employ parallel transmission, they generally have more pins and the width of the cable tends to be larger. Additionally, the length of the cable is limited in order to achieve simultaneous transmission. Whereas, the SATA hard disks employ serial transmission, so the number of pins thereof is smaller, the length of the cable is larger and it is easier to install. Furthermore, the speed of the SATA hard disks is greater, up to 150 MB/s, and multi-links are allowed which increases transmission speed. In the future, the SATA hard disks may become the mainstream products in the market, replacing the PATA hard disks.
During system booting, when the power is turned on, the hard disks immediately begins to operate. Each hard disk has a startup current, e.g. up to about 2 Amps (A) for a single hard disk. When the system is only connected to a single hard disk, the transient peak current of a power supply of the system is the startup current (i.e. 2A) of the hard disk. When the hard disk operates towards a steady state, the current consumed by the hard disk then reduces to a lower average value. If the number of hard disks connected to the system is small, the peak current at startup does not significantly affect the power supply. However, under the demands of ever larger storage capacity, the system tends to attach to more hard disks. In this case, the total peak current generated by these hard disks all starting up at the same time may now significantly affect the power supply. For example, a server system may be connected to up to 12 hard disks. When all 12 hard disks start up simultaneously, the total transient peak current may be as high as 24 A. The total transient peak current in this case may exceed the over-current protection threshold value of the power supply, causing system shutdown and boot failure. As described above, when 12 hard disks start up simultaneously, the total transient peak current may be as high as 24 A, an ordinary power supply cannot withstand such a high transient peak current, and may be easily burnt. In such case, a specialized and more expensive power supply is required, however, this increases cost.
Therefore, there is a need for a technique to control startup of hard disks sequentially in order to eliminate the situation of simultaneously startup of a plurality of hard disks that causes system boot failure or power supply burnt down.